Parking brake system for a work vehicle

ABSTRACT

A work vehicle includes a vehicle body frame, an electric motor supported by the vehicle body frame, a power transmission mechanism including a drive shaft connected to an output shaft of the electric motor to transmit power generated by the electric motor to a wheel on which a tire is mounted, a supporting member supported by the vehicle body frame to rotatably support the drive shaft, and a parking brake provided on an outside of the supporting member to restrict a rotation of the drive shaft.

This application is related to co-pending application: “WORK VEHICLE” filed on Feb. 26, 2018, U.S. Ser. No. 15/755,236, in the names of Shinichi NAITOU and Takuya ISHIZAKA as a national phase entry of PCT/JP2016/058333 filed Mar. 16, 2016, which application is assigned to the assignee of the present application and is incorporated by reference herein.

FIELD

The present invention relates to a work vehicle.

BACKGROUND

In a technological field relating to work vehicles, a large autonomous off-road dump truck as disclosed in Patent Literature 1 is known.

CITATION LIST Patent Literature

Patent Literature 1: WO 2015/129005 A

SUMMARY Technical Problem

For a work vehicle which is provided with a parking brake, a technology to facilitate maintenance of the parking brake has been demanded.

An object of the aspects of the present invention is to provide a work vehicle having a parking brake which is readily maintained.

Solution to Problem

According to an aspect of the present invention, a work vehicle comprises: a vehicle body frame; an electric motor supported by the vehicle body frame; a power transmission mechanism including a drive shaft connected to an output shaft of the electric motor to transmit power generated by the electric motor to a wheel on which a tire is mounted; a supporting member supported by the vehicle body frame to rotatably support the drive shaft; and a parking brake provided on an outside of the supporting member to restrict a rotation of the drive shaft.

Advantageous Effects of Invention

According to an aspect of the present invention, a work vehicle having a parking brake which is readily maintained is provided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an exemplary side view of a work vehicle according to the present embodiment.

FIG. 2 is an exemplary view of the work vehicle according to the present embodiment viewed in a +X direction.

FIG. 3 is an exemplary cross-sectional view of a travel unit according to the present embodiment.

FIG. 4 is an exemplary cross-sectional view of a cooling structure for electric motors according to the present embodiment.

FIG. 5 is an exemplary plan view of a parking brake according to the present embodiment.

FIG. 6 is an exemplary cross-sectional view of the parking brake according to the present embodiment.

FIG. 7 is an exploded perspective view of part of the parking brake according to the present embodiment.

FIG. 8 is a cross-sectional view of part of the parking brake according to the present embodiment.

DESCRIPTION OF EMBODIMENTS

The embodiments according to the present invention will be described below with reference to the drawings, but the present invention is not limited to the description. The component elements of the embodiments described below may be appropriately combined with each other. Furthermore, some of the component elements may not be used.

In the following description, an X-Y-Z rectangular coordinate system is set, and a positional relationship between units will be described with reference to the X-Y-Z rectangular coordinate system. A direction parallel to a first axis in a predetermined plane is represented as an X-axis direction, a direction parallel to a second axis in the predetermined plane perpendicular to the first axis is represented as a Y-axis direction, and a direction parallel to a third axis perpendicular to the predetermined plane is represented as a Z-axis direction.

[Dump Truck]

FIG. 1 is an exemplary side view of a work vehicle 1 according to the present embodiment. FIG. 2 is an exemplary view of the work vehicle 1 according to the present embodiment viewed in a +X direction. In the present embodiment, the work vehicle 1 is a dump truck which is loaded and travels in a mining site. The dump truck is an off-road dump truck which is remotely controlled to autonomously travel. The dump truck has no cab. The dump truck includes a communication device communicating with a control station. The control station transmits a command signal to the dump truck to remotely control the dump truck. In the following description, the work vehicle 1 is referred to as a dump truck 1.

In the present embodiment, the dump truck 1 travels in the +X direction for ease of description. The X-axis direction represents a front-rear direction of the dump truck 1, the Y-axis direction represents a vehicle width direction of the dump truck 1, and the Z-axis direction represents a vertical direction of the dump truck 1.

As illustrated in FIGS. 1 and 2, the dump truck 1 includes a vehicle body 10, a dump body 30 supported by the vehicle body 10, and a travel unit 40 supported by a vehicle body frame 20 of the vehicle body 10.

The travel unit 40 includes wheels 11 on which tires 11T are mounted, and electric motors 43 for generating power to drive the respective wheels 11. The wheels 11 include a wheel 11F disposed forward of the center of the vehicle body frame 20 and a wheel 11R disposed backward of the center of the vehicle body frame 20. The wheels 11F are disposed on both sides in a vehicle width direction. The wheels 11R are disposed on both sides in a vehicle width direction. Four electric motors 43 are provided to drive four wheels 11 individually.

The dump body 30 is a loaded member. The dump body 30 is rotatable about a pivot portion 37 by the operation of a hoist cylinder. As indicated by a two-dot chain line in FIG. 1, the dump body 30 performs dumping operation to unload material on the dump body 30 from the dump body 30.

[Travel Unit]

FIG. 3 is an exemplary cross-sectional view of the travel unit 40 according to the present embodiment. As illustrated in FIGS. 1, 2, and 3, the travel unit 40 includes the electric motors 43, and power transmission mechanisms 45 each including a drive shaft 18 connected to an output shaft 43A of each electric motor 43 and a decelerator 14 connected to the drive shaft 18. The decelerator 14 is at least partially connected to the wheel 11. The power transmission mechanism 45 including the drive shaft 18 and the decelerator 14 transmits power generated by the electric motor 43 to the wheel 11.

The vehicle body frame 20 includes vertical frames 21 for supporting the electric motors 43. The vertical frames 21 include a vertical frame 21F for supporting the electric motors 43 for generating power to drive the wheels 11F, and a vertical frame 21R for supporting the electric motors 43 for generating power to drive the wheels 11R. The vertical frame 21F is provided at a front portion of the vehicle body frame 20. The vertical frame 21R is provided at a rear portion of the vehicle body frame 20. One vertical frame 21 supports two electric motors 43.

As illustrated in FIG. 1, the vertical frame 21F and the vertical frame 21R are connected to each other via a lower side member 23 and an upper side member 24. Furthermore, as illustrated in FIGS. 1 and 2, the vehicle body frame 20 includes a pair of side members 25 disposed at lower portions of each vertical frame 21 in the vehicle width direction, and cross members 26 coupling the pair of side members 25.

The vertical frame 21 includes a lower cross member 201, vertical members 202, and an upper cross member 203. The lower cross member 201 extends in a vehicle width direction. The upper cross member 203 is positioned above the lower cross member 201 and extends in the vehicle width direction. Each vertical member 202 extends in a vertical direction to connect an end portion of the lower cross member 201 and an end portion of the upper cross member 203 to each other. The dump body 30 is supported by the upper cross member 203.

The electric motor 43 includes a motor housing 43H supported by the vertical frame 21 of the vehicle body frame 20. In the present embodiment, the motor housing 43H of the electric motor 43 is supported by the lower cross member 201 of the vehicle body frame 20. The lower cross member 201 is a hollow member having an inner space. The electric motor 43 is at least partially stored in the inner space of the lower cross member 201.

The drive shaft 18 is connected to the output shaft 43A of the electric motor 43 and transmits power generated by the electric motor 43 to the decelerator 14.

The decelerator 14 transmits the power of the electric motor 43 transmitted via the drive shaft 18, to the wheel 11. The decelerator 14 includes a planetary gear mechanism to convert a high-speed, low-torque rotational force of the electric motor 43 to a low-speed, high-torque rotational force and transmit the rotational force to the wheel 11.

The power transmission mechanism 45 including the drive shaft 18 and the decelerator 14 is at least partially disposed on the inside of the wheel 11.

The travel unit 40 includes a brake 15 disposed on the inside of the wheel 11 to restrict the rotation of the wheel 11. The brake 15 has a wet oiling brake.

Furthermore, the travel unit 40 includes a drive case 56 for storing at least part of the power transmission mechanism 45. The drive case 56 is disposed on the inside of the wheel 11. The drive case 56 is partially connected to the wheel 11. The planetary gear mechanism of the decelerator 14 has a sun gear connected to the drive shaft 18, and has a planetary gear connected to part of the drive case 56. The decelerator 14 rotatably supports the wheel 11 via the drive case 56. In the present embodiment, the decelerator 14 and the drive shaft 18 are partially stored in the drive case 56. The drive shaft 18 is partially disposed outside the drive case 56.

The travel unit 40 includes a suspension 50. In the present embodiment, the suspension 50 is an independent double wishbone suspension system. The suspension 50 includes a suspension cylinder 53 and a link mechanism 60 which is configured to connect the vehicle body frame 20 and the drive case 56 to each other.

The suspension cylinder 53 connects the vehicle body frame 20 and the drive case 56 to each other. In the present embodiment, the suspension cylinder 53 has an upper end portion connected to a suspension supporting portion 205 provided at the upper cross member 203. The suspension cylinder 53 has a lower end portion connected to the drive case 56 via a connection bracket 54. The suspension cylinder 53 absorbs or damps an impact on a tire 11T.

The link mechanism 60 connects the vehicle body frame 20 and the drive case 56 to each other so as to separate the vehicle body frame 20 from the wheel 11. Owing to the link mechanism 60, the vehicle body frame 20 opposes the wheel 11 and the tire 11T across a gap, and a space is formed between the vehicle body frame 20 and the wheel 11 and tire 11T. The space between the vehicle body frame 20 and the wheel 11 and the tire 11T is an open space opening to an ambient space.

The link mechanism 60 includes an upper arm 51 which has a base end portion connected to the vehicle body frame 20 and has a leading end portion connected to an upper portion of the drive case 56, and a lower arm 52 which has a base end portion connected to the vehicle body frame 20 and a leading end portion connected to a lower portion of the drive case 56. The upper arm 51 and the lower arm 52 each extend in a substantially horizontal direction. The base end portion of the upper arm 51 is vertically swingably supported by the vehicle body frame 20. The base end portion of the lower arm 52 is vertically swingably supported by the vehicle body frame 20. The upper portion of the drive case 56 is rotatably connected to the leading end portion of the upper arm 51. The lower portion of the drive case 56 is rotatably connected to the leading end portion of the lower arm 52.

In the present embodiment, the base end portion of the upper arm 51 is rotatably supported by an upper supporting portion 207 provided at a lower portion of the vertical member 202 of the vertical frame 21. The base end portion of the lower arm 52 is rotatably supported by a lower supporting portion 208 provided at an end portion of the lower cross member 201.

The leading end portion of the upper arm 51 is connected to an upper ball joint 57 provided at the upper portion of the drive case 56. The leading end portion of the lower arm 52 is connected to a lower ball joint 58 provided at the lower portion of the drive case 56. The upper ball joint 57 has an upper surface to which the connection bracket 54 is fixed. The connection bracket 54 and the suspension supporting portion 205 of the vertical frame 21 are connected to each other by the suspension cylinder 53.

When the vehicle body 10 is swung in a vertical direction with swinging of the upper arm 51 and the lower arm 52, a positional relationship between the wheel 11 and the electric motor 43 is slightly shifted. In the present embodiment, the drive shaft 18 is connected to each of the output shaft 43A of the electric motor 43 and an input shaft 14A of the decelerator 14 via a universal joint. Therefore, even if the vehicle body 10 is swung in the vertical direction, a shift between the wheel 11 and the electric motor 43 is absorbed. Furthermore, in the present embodiment, the drive shaft 18 is telescopically slidable in the axial direction. Therefore, a change in the distance between the vehicle body frame 20 and the drive case 56 caused by swinging of the wheel 11 in the vertical direction is absorbed.

The dump truck 1 includes parking brakes 100. Each of the parking brakes 100 restricts the rotation of the corresponding wheel 11 during parking of the dump truck 1. In the present embodiment, the parking brake 100 restricts the rotation of the drive shaft 18 to restrict the rotation of the wheel 11.

The parking brake 100 is disposed in a space between the vehicle body frame 20 and the wheel 11, formed by the link mechanism 60.

[Cooling Structure of Electric Motor]

FIG. 4 is an exemplary cross-sectional view of a cooling structure for electric motors 43 according to the present embodiment. As illustrated in FIG. 4, the electric motors 43 are disposed on both sides of the lower cross member 201 in a vehicle width direction. On both sides of the lower cross member 201 in the vehicle width direction, opening portions 209 are provided. The electric motors 43 are disposed at least partially in the respective opening portions 209. The motor housing 43H of each electric motor 43 and the lower cross member 201 of the vehicle body frame 20 are fixed to each other.

The inner space of the lower cross member 201 has projection portions 210. Each of the projection portions 210 projects from an inner surface of the inner space of the lower cross member 201 toward the electric motor 43. A plurality of projection portions 210 is spaced apart around the motor housing 43H. The motor housing 43H of the electric motor 43 is partially supported by the projection portions 210.

The lower cross member 201 has a center portion in the vehicle width direction, where an inlet 211 is provided. The inlet 211 is provided in an upper portion of the lower cross member 201. Above the lower cross member 201, a cooling blower 71 is disposed. The cooling blower 71 delivers cooling air. The cooling air sent from the cooling blower 71 is supplied into the inner space of the lower cross member 201 via the inlet 211.

Cooling air is supplied from the cooling blower 71 to the inner space of the lower cross member 201 via the inlet 211, flows into a duct portion 72 positioned between a pair of the electric motors 43, and then flows toward the electric motors 43. Cooling air partially flows into spaces between the electric motors 43 and an inner surface of the lower cross member 201, cools the outer surfaces of the motor housings 43H of the electric motors 43, and then flows outside the lower cross member 201 via gaps between the motor housings 43H and the opening portions 209. Furthermore, cooling air partially flows into the motor housings 43H, cools a stator, a mover, and the like of each electric motor 43, and then flows outside each motor housing 43H via a gap provided in at least part of the motor housing 43H.

[Parking Brake]

FIG. 5 is an exemplary plan view of the parking brake 100 according to the present embodiment. FIG. 6 is an exemplary cross-sectional view of the parking brake 100 according to the present embodiment. FIG. 7 is an exploded perspective view of part of the parking brake 100 according to the present embodiment.

As illustrated in FIG. 5, the parking brake 100 is a member disposed around a rotation axis AX. As illustrated in FIG. 6, the output shaft 43A of the electric motor 43 is at least partially stored in the motor housing 43H. The output shaft 43A of the electric motor 43 and the drive shaft 18 of the power transmission mechanism 45 are connected to each other via a connection shaft 47. Note that the connection shaft 47 and the drive shaft 18 may be considered to be integrated with each other.

The drive shaft 18 is rotatably supported by a supporting member 81 via bearings 80. The supporting member 81 rotatably supports the drive shaft 18 about the rotation axis AX. The supporting member 81 is fixed to the motor housing 43H. The supporting member 81 is supported by the vehicle body frame 20 via the motor housing 43H.

In the present embodiment, the supporting member 81 is a bearing case for storing the bearings 80 for rotatably supporting the drive shaft 18. In the following description, the supporting member 81 is referred to as a bearing case 81. In the present embodiment, the bearing case 81 includes a first case member 81A and a second case member 82B.

In a direction parallel to the rotation axis AX, one of the bearings 80 is provided with an oil seal 82 and the other of the bearings is provided with an oil seal 83. The oil seal 82 and the oil seal 83 seal between the connection shaft 47 and the bearing case 81.

The parking brake 100 is provided on the outside of the bearing case 81. Note that the parking brake 100 may be provided at the motor housing 43H. In this configuration, the motor housing 43H serves as the supporting member.

The parking brake 100 includes a disk 104 supported by a hub 102, a separator plate 106 supported by a cylinder 110, an end plate 108 fixed to the cylinder 110 by a pin, a piston 112 movable relative to the cylinder 110 in a direction parallel to the rotation axis AX, a cylinder plate 114 fixed to the cylinder 110, and a dust seal 116 for sealing between the piston 112 and the cylinder plate 114.

The hub 102 is fixed to the connection shaft 47 and the drive shaft 18 via a coupling 84.

The disk 104 is supported by the hub 102. As illustrated in FIG. 7, the disk 104 is an annular member disposed so as to surround the rotation axis AX. A plurality of disks 104 is spaced apart in a direction parallel to the rotation axis AX.

The separator plate 106 is supported by the cylinder 110. As illustrated in FIG. 7, the separator plate 106 is an annular member disposed so as to surround the rotation axis AX. A plurality of separator plates 106 is spaced apart in a direction parallel to the rotation axis AX. The separator plates 106 are disposed between the disks 104. The separator plates 106 are at least partially disposed radially outwardly from the disks 104 relative to the rotation axis AX.

The cylinder 110 is fixed to the bearing case 81 via the end plate 108. Note that the cylinder 110 may be fixed to the motor housing 43H via the end plate 108.

The piston 112 includes a first member 112A disposed to make contact with a separator plate 106, and a second member 112B for forming a gap between the second member 112B and the cylinder plate 114 to dispose the dust seal 116 therebetween. As illustrated in FIG. 7, the piston 112 (first member 112A) is an annular member disposed so as to surround the rotation axis AX.

In the present embodiment, when the electric motor 43 is operated, the output shaft 43A, the connection shaft 47, and the drive shaft 18 are rotated about the rotation axis AX. When the connection shaft 47 is rotated, the coupling 84, the hub 102, and the disks 104, all of which are fixed to the connection shaft 47, are rotated about the rotation axis AX, together with the output shaft 43A, the connection shaft 47, and the drive shaft 18. That is, the output shaft 43A, the connection shaft 47, the drive shaft 18, the coupling 84, the hub 102, and the disks 104 are a rotator rotated by the operation of the electric motor 43.

In contrast, the motor housing 43H, the bearing case 81, the separator plates 106, the end plate 108, the cylinder 110, the piston 112, and the cylinder plate 114 are a stator not rotated when the electric motor 43 is operated.

The piston 112 is moved in a direction parallel to the center axis AX by a hydraulic pressure supplied from a hydraulic pressure supply device 118. In the present embodiment, oil is supplied from the hydraulic pressure supply device 118 into a space between the piston 112 and the cylinder 110, and when a hydraulic pressure is applied to the piston 112, the piston 112 is moved to be separated from the separator plate 106.

FIG. 8 is a cross-sectional view of part of the parking brake 100 according to the present embodiment. FIG. 8 illustrates the parking brake 100 where no hydraulic pressure is applied to the piston 112. In the present embodiment, a spring 120 is disposed between the piston 112 and the cylinder plate 114. The spring 120 generates a resilient force so that the piston 112 comes closer to the separator plate 106.

As illustrated in FIG. 8, when no hydraulic pressure is applied to the piston 112, the piston 112 is moved to come closer to the separator plate 106 by the resilient force of the spring 120. When the piston 112 is moved toward the separator plate 106, the separator plate 106 is displaced. Therefore, the plurality of separator plates 106 and the plurality of disks 104 are brought into contact with each other, as illustrated in FIG. 8. Therefore, the rotation of the disks 104 is suppressed. The suppression of the rotation of the disks 104 restricts the rotation of the rotator including the output shaft 43A, the connection shaft 47, the drive shaft 18, the coupling 84, the hub 102, and the disks 104.

That is, in the present embodiment, when the supply of a hydraulic pressure from the hydraulic pressure supply device 118 is stopped, the parking brake 100 restricts the rotation of the drive shaft 18.

In contrast, when a hydraulic pressure is supplied from the hydraulic pressure supply device 118, the piston 112 is moved to be separated from the separator plate 106. When the piston 112 is moved to be separated from the separator plate 106, the separator plate 106 is displaced. Therefore, the plurality of separator plates 106 and the plurality of disks 104 are separated from each other, as illustrated in FIG. 6. Therefore, braking by the parking brake 100 is released.

[Functions and Effects]

As described above, according to the present embodiment, the parking brake 100 is supported by the supporting member 81 supported by the vehicle body frame 20 and rotatably supporting the drive shaft 18. Accordingly, the parking brake 100 is provided between the vehicle body frame 20 and the wheel 11. A worker can readily access the space between the vehicle body frame 20 and the wheel 11. Therefore, providing the parking brake 100 between the vehicle body frame 20 and the wheel 11 allows the worker to readily access the parking brake 100, and thus the parking brake 100 may be readily maintained.

Furthermore, in the present embodiment, the drive case 56 of the power transmission mechanism 45, disposed in the wheel 11, is connected to the vehicle body frame 20 by using the link mechanism 60 of the suspension 50. The drive case 56 is connected to the vehicle body frame 20 by using the link mechanism 60, and a sufficiently large space opening to the ambient space is formed between the vehicle body frame 20 and the wheel 11. Disposing the parking brake 100 in the sufficiently large open space formed between the vehicle body frame 20 and the wheel 11 allows the worker to ensure a sufficiently large work space around the parking brake 100, enabling working of a plurality of workers.

Furthermore, in the present embodiment, the supporting member 81 for supporting the parking brake 100 is the bearing case 81 configured to store the bearings 80 for rotatably supporting the drive shaft 18. The bearing case 81 is supported by the vehicle body frame 20 via the motor housing 43H. The parking brake 100 is supported by the bearing case 81 configured to store the bearings 80 for rotatably supporting the drive shaft 18, and thus the parking brake 100 can be readily maintained from outside without increasing the weight of the vehicle body frame 20. For example, if the parking brake 100 is provided in the vehicle body frame 20, the vehicle body frame 20 needs to be provided with a maintenance hole for accessing the parking brake 100 in the vehicle body frame 20. Addition of a reinforcement member for compensating for a reduction in strength of the vehicle body frame 20 caused by the hole may rather increase the weight of the vehicle body frame 20. According to the present embodiment, the parking brake 100 is supported by the bearing case 81, and thus a high maintainability of the parking brake 100 can be ensured without increasing the weight of the vehicle body frame 20.

Note that, in the present embodiment, the parking brake 100 is a dry condition brake. The parking brake 100 may be a wet oiling brake, and another brake may be further adapted as long as the adapted brake has a mechanism for stopping the rotation of the drive shaft 18.

Note that the dump truck 1 according to the present embodiment is a four-wheel-drive dump truck which is provided with the electric motors 43 for the respective four wheels 11. The electric motor 43 may be provided at either the wheels 11F or the wheels 11R. Note that the dump truck 1 according to the present embodiment may be a four wheel steered dump truck.

Note that, in the present embodiment, the dump truck 1 is an autonomous off-road dump truck which autonomously travels. The dump truck 1 may be a manned off-road dump truck provided with a cab and operated by a driver in the cab.

Note that, in the present embodiment, the work vehicle 1 is a dump truck having the dump body 30. The work vehicle 1 may be, however, a vehicle without the dump body 30.

REFERENCE SIGNS LIST

1 DUMP TRUCK (WORK VEHICLE)

10 VEHICLE BODY

11 WHEEL

11F WHEEL

11R WHEEL

11T TIRE

14 DECELERATOR

15 BRAKE

14A INPUT SHAFT

18 DRIVE SHAFT

20 VEHICLE BODY FRAME

21 VERTICAL FRAME

21F VERTICAL FRAME

21R VERTICAL FRAME

23 LOWER SIDE MEMBER

24 UPPER SIDE MEMBER

25 SIDE MEMBER

26 CROSS MEMBER

30 DUMP BODY

37 PIVOT PORTION

40 TRAVEL UNIT

43 ELECTRIC MOTOR

43A OUTPUT SHAFT

43H MOTOR HOUSING

45 POWER TRANSMISSION MECHANISM

47 CONNECTION SHAFT

50 SUSPENSION

51 UPPER ARM

52 LOWER ARM

53 SUSPENSION CYLINDER

54 CONNECTION BRACKET

56 DRIVE CASE

57 UPPER BALL JOINT

58 LOWER BALL JOINT

60 LINK MECHANISM

71 COOLING BLOWER

72 DUCT PORTION

80 BEARING

81 BEARING CASE (SUPPORTING MEMBER)

82 OIL SEAL

83 OIL SEAL

84 COUPLING

100 PARKING BRAKE

102 HUB

104 DISK

106 SEPARATOR PLATE

108 END PLATE

110 CYLINDER

112 PISTON

112A FIRST MEMBER

112B SECOND MEMBER

114 CYLINDER PLATE

116 DUST SEAL

118 HYDRAULIC PRESSURE SUPPLY DEVICE

120 SPRING

201 LOWER CROSS MEMBER

202 VERTICAL MEMBER

203 UPPER CROSS MEMBER

205 SUSPENSION SUPPORTING PORTION

207 UPPER SUPPORTING PORTION

209 OPENING PORTION

210 PROJECTION PORTION

211 INLET

AX ROTATION AXIS 

The invention claimed is:
 1. A work vehicle comprising: a vehicle body frame; an electric motor supported by the vehicle body frame; a power transmission mechanism including a drive shaft connected to an output shaft of the electric motor to transmit power generated by the electric motor to a wheel on which a tire is mounted; a supporting member supported by the vehicle body frame to rotatably support the drive shaft; and a parking brake provided on an outside of the supporting member to restrict a rotation of the drive shaft.
 2. The work vehicle according to claim 1, further comprising: a drive case disposed on an inside of the wheel to store at least part of the power transmission mechanism; and a link mechanism configured to connect the vehicle body frame and the drive case to each other to separate the vehicle body frame from the wheel, wherein the parking brake is disposed between the vehicle body frame and the wheel.
 3. The work vehicle according to claim 1, wherein the supporting member includes a bearing case storing a bearing configured to rotatably support the drive shaft, and is supported by the vehicle body frame via a motor housing of the electric motor. 